Microbiological Diagnostic Methods and Spectrum of Fungal Keratitis in Eastern Nepal

The most useful and the quickest diagnostic method for assessing fungal components in corneal scrapings in low-resource settings is microscopic assessment.

The aim of this study was to compare the diagnostic sensitivity of potassium hydroxide (KOH) and potassium hydroxide + calcofluor white (KOH+CFW) staining for detecting fungal keratitis (FK) using culture as the standard of reference, as well as to analyse their fungal culture results.

This was a retrospective study where consecutive patients with microbial keratitis (MK) attending Biratnagar Eye Hospital from 2023 January to 2023 December were recruited. Corneal scrapes were sent for microscopic examination and culture using the standard protocol. Smear microscopy was performed using KOH wet mount, Gram stain, and KOH+CFW stain to determine the presence of microbial components in corneal scrapings. The sensitivity of KOH and KOH+CFW in diagnosing FK was compared.

Among the 2,152 samples examined, 1,507 (70.02%) had pure fungal infections, 121 (5.62%) had pure bacterial infections, and 41 (1.9%) had mixed aetiology (bacteria + fungus). Smear microscopy revealed Acanthamoeba keratitis in eight (0.37%) samples. Direct microscopy of corneal scrapes revealed fungal elements in 1,420 (65.98%) and 1,523 (70.77%) from KOH and KOH+CFW preparations, respectively. Fungal culture was positive in 1,041 (48.37%) samples tested. The sensitivity of KOH+CFW (97.69%) was shown to be significantly higher than that of KOH alone (95.19%) (p = 0.0013) in diagnosing FK. Curvularia spp. was the most frequently isolated fungus, with 312/1,041 (29.97%) of positive fungal cultures.

KOH+CFW stain demonstrated to be more sensitive than KOH stain, as a point-of-care diagnostic tool for FK. Fluorescence microscopy with the KOH+CFW stain is recommended as a routine procedure in cases of MK in areas where FK is highly prevalent.